The present invention relates to improved acoustic transducers having a diaphragm of the type where the entire surface is driven, which are designed for use in loudspeakers, earphones, head phones or microphones.
For example, in U.S. Pat. No. 3,919,498 specification there is described an acoustic transducer having a conductor and a vibratable flat diaphragm disposed in a magnetic field defined by a permanent magnet. The transducer of this type has the flat diaphragm fixed to the confronting magnet at its entire periphery and its center by means of a suitable fixing member. This transducer has a disadvantage in that since the entire surface of the diaphragm is not driven, the amplitude of the diaphragm is so small that a low sound frequency range cannot faithfully be reproduced. There is also known an acoustic transducer having a corrugated diaphragm having a number of elongate, rectangular sections. A disadvantage of the transducer of this type is that the diaphragm does not vibrate as a unit while undergoing partial deformation, resulting in unfaithful sound reproduction. This is because the central portions of the flat portions forming part of the corrugated diaphragm are expanded and deformed in the direction opposite to vibrations due to air resistance and inertia, and that the thus expanded and deformed portions are subjected to restoration by decreases in the air resistance and the elasticity of the flat portions at the lower and upper limits of vibrations.
A main object of the present invention is therefore to provide an acoustic transducer free from such disadvantages.
In accordance with the present invention, the diaphragm comprises a thin film member corrugated to form a number of elongate, arcuate corrugations and conductors provided on the respective trough portions of the corrugations in series relation thereto. Permanent magnets adapted to produce magnetic fluxes in the direction extending perpendicularly to the conductors on the respective trough portions are retained between the respective trough portions, and both surfaces of each side edge portions of the diaphragm are carried by support members which are expandable and contrictable only in the direction normal to the diaphragm. With such an arrangement, it is possible to prevent the diaphragm from suffering any deformation due to the air pressure caused by its vibrations and inertia. In addition, even when the diaphragm is partially deformed, no restoration of the thus deformed portion takes place at the end of vibrations. The expandability and restorability of the support members make it possible to increase the amplitude of the travel of the diaphragm and to uniformly oscillate the diaphragm over its entire surface and in the same phase, thus leading to faithful reproduction of a low sound range and increases in the allowable input.
The above and other objects and advantages will be clear from the following detailed description of exemplary preferred embodiments illustrated in the appended drawing.